The present invention generally relates to semiconductor processing and, more particularly, to a system and method for measuring and/or imaging features, such as lines and spaces, including those having a re-entrant profile.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers (e.g., at submicron levels). In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, etc.) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist, Scanning Electron Microscopes (SEMs) often are employed to analyze and measure critical dimensions resulting from the lithographic process. Critical dimensions include the size of minimum features across the wafer such as linewidth, spacing, and contact dimensions.
In certain fabrication processes, resist and/or etched features have cross-sectional profiles that are re-entrant. By xe2x80x9cre-entrant profile,xe2x80x9d it is meant that the sidewalls of the feature taper inwardly at the bottom of the feature. For an elongated feature, such as a line or space, a re-entrant profile may result in an elongated trench (e.g., having a triangular cross section) positioned along the juncture of the feature and the substrate surface parallel to the substrate surface. While the re-entrant profile may be desirable in certain circumstances, the re-entrant features may cause a shadowing effect during subsequent deposition. As a result of the shadowing effect by the upper portion of the feature, an elongated void may be formed during the deposition at the bottom surface of the re-entrant feature in contact with the substrate. The void, if undetected, may have serious consequences for subsequent processing steps and may result in defects that compromise the operation of the resulting semiconductor device. Conventional SEM systems for measuring critical dimensions of wafers often fail to detect re-entrant profiles of lines and/or spaces, as they tend to employ top-down electron beams or a beam that is electronically tilted at a predetermined angle relative to the substrate.
It is desirable to have a system and/or method which facilitates measuring and/or imaging a feature, such as a line and/or space, having a re-entrant profile.
The present invention relates to a system and method for measuring and/or imaging a feature having a re-entrant cross-sectional profile. Beams are emitted onto the feature and substrate at at least two different angles during corresponding measurement intervals, such as by employing a scan-tilt CD-SEM. A feature data set for the feature is characterized for each measurement interval. The data sets associated with each measurement interval are aggregated to provide a cross-sectional representation of the feature. Because beams are emitted at different relative angles during the measurement intervals, each corresponding data set represents feature characteristics according to portions of the feature that the beam strikes. As a result, a more accurate feature profile may be determined, including a cross-sectional dimension of the feature at the juncture between the feature and substrate.
One aspect of the present invention relates to a method for measuring a cross-sectional profile of a feature in a substrate. The method includes the steps of performing first and second scans of the feature at different angles relative to the substrate to provide respective first and second feature data sets, such that an aggregate of the first and second feature data sets indicates the feature profile.
Another aspect of the present invention relates to a system for determining a cross-sectional profile of a feature in a substrate. An emitter directs a beam onto the substrate at a first angle during a first measurement interval and at a second angle, which is different from the first angle, during a second measurement interval. A detector detects interactions between the beam and the feature and/or substrate and provides a detector signal indicative thereof. A controller determines a first feature data set based on the detector signal associated with the first measurement interval and a second feature data set based on the detector signal associated with the beam during the second measurement interval. The controller then determines a cross-sectional characteristic of the feature based on the first and second feature data sets.
Yet another aspect of the present invention relates to a CD-SEM system primarily for measuring a cross-sectional dimension of a feature having a re-entrant profile relative to a substrate. A lens is provided for directing electrons to the surface of the substrate at a first angle during a first scanning interval and at a second angle during a second scanning interval, the second angle being different from the first angle relative to the substrate. A detector provides a signal based upon electrons received from the surface of the wafer. A processing system determines a first feature data set based on detected electrons associated with the first scanning interval and a second feature data set based on detected electrons associated with the second scanning interval. The processing system determines a cross-sectional characteristic of the feature based on an aggregation of the first and second feature data sets.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.